1. Field of the Invention
The present invention relates to a light source unit for use in a laser beam printer, a copying apparatus, a facsimile apparatus, a phototype setting apparatus, a bar code reading apparatus, and a sensor, and to its manufacturing method, adjusting method and adjusting apparatus.
2. Description of the Prior Art
Light source units constituted by semiconductor lasers (for example, laser diodes) are used as laser beam irradiating apparatuses for forming images such as letters on a photoreceptor drum at a high speed in image forming apparatuses such as laser beam printers, copying apparatuses and facsimile apparatuses. In phototype setting apparatuses, light source units are used as laser beam apparatuses for high-speed printing onto film. In bar code reading apparatuses and various sensors, light source units are used as laser beam irradiating apparatuses for obtaining information from bar codes and light beams reflected by an object.
In well-known, typical apparatuses using the above-mentioned light source unit, one laser beam is formed by a pair consisting of a semiconductor laser and a lens which serves as a collimator, and the laser beam is reflected by a polygonal scanner to form an image on a predetermined surface.
In such an arrangement using one semiconductor laser, since a processing speed depends on a scanning speed, it is impossible to increase the processing speed beyond a limit.
To solve such a problem, an apparatus has been proposed where two or three monolithic laser stripes are formed and two or three light emitting points are provided in one package. With this arrangement, it is possible to generate two or three laser beams for scanning. As a result, the processing speed can be realized which is two or three times the processing speed of the apparatus where only one semiconductor laser is used.
In the above-described arrangement where a plurality of monolithic laser stripes are generated, however, it is difficult to cause all the laser stripes to emit laser beams with an equal intensity. If, in order to solve this problem, laser emission were controlled by monitoring a laser beam emitted from a rear end surface of each semiconductor laser by use of a corresponding photodiode, the monitored laser beams would overlap one another and it would be difficult to separate the monitors into each monitored laser beam.
Moreover, in an arrangement where a plurality of monolithic laser stripes are formed as described above, it is necessary to increase the number of leads accordingly. Since the number of light emitting points in one package is limited, the processing speed can be increased by only several times.
Further, in the previously-described typical light source unit, the semiconductor laser and the collimator lens are normally fixed to a fixing member through laser welding.
FIG. 1 shows a manner in which a semiconductor laser 220 is fixed to a body 230 which serves as a fixing member through YAG laser welding. The YAG laser welding is performed by irradiating one YAG laser beam LB onto a boundary (welding point P) of the body 230 and the semiconductor laser 220 from a YAG laser irradiating nozzle unit 210.
The welding point P (with a diameter of approximately 0.3 mm) which is momentarily melted shrinks while it is cooled and hardened again. The semiconductor laser 220 is drawn by a resultant force, and shifts toward the side of the welding point P. The movement amount thereof ranges from approximately 1 .mu.m to several tens of microns.
As a result, even if fine positioning of approximately 1 .mu.m order is performed with respect to the semiconductor laser 220, the laser 220 is fixed under a condition where there is a position shift through the succeeding laser welding. Moreover, when a lens is fixed to the body 230, a similar problem arises in fixing to the body 230 a lens barrel to which the lens is fixed.